Delta has a mixed fleet of 767s with both Pratts & GEs. Why, I don't know.
Northwest had DC-10s with Pratts (series 40) & 2nd-tier series 30s with GEs.
When the 707 was flying, there were carriers using both Pratts on the -320s & RR Conways on the -420s...I think British Airways was one of them.
There are more out there, but this is all I can think of at the moment. Regards.

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